In recent years, introduction of a passive optical network (PON) system as an optical access system that supports a rapidly spreading Fiber to the Home (FTTH) service has progressed worldwide. In a PON system, one optical line terminal (OLT) disposed in a housing station accommodates optical network units (ONU) disposed in a plurality of subscriber homes through an optical splitter disposed in the middle of an optical fiber transmission line. The PON system is an optical access system that realizes high economic efficiency by sharing optical fiber transmission lines, an optical splitter, and OLTs among a plurality of subscribers.
At present, in Japan, a Gigabit Ethernet-PON (GE-PON) system having a transmission quantity of 1 Gb/s has been mainly commercially introduced (Ethernet is a registered trademark). In addition, as a next-generation optical access system realizing a higher speed, standardization of 10 G-EPON and XP-PON having a total transmission capacity of a 10 Gb/s level has been completed, and research and development thereof are progressing worldwide.
In light of such an increase in the transmission speed, as a next PON system at the 10 Gb/s level, NG-PON2 has been discussed on the Full Service Access Network (FSAN) forum. In the NG-PON2, in addition to an increase in speed from that of a conventional PON system, improvement of the access network is set as a goal. As the NG-PON2, a time and wavelength-division multiplexing (TWDM)-PON system has been reviewed. The TWDM-PON system is able to achieve an increase in accommodating efficiency, efficiency of maintenance management and the like by using wavelength-division multiplexing (WDM) utilizing characteristics of light in addition to time division multiplexing (TDM) that has been used in a conventional PON system.